1. Technical Field
The present invention relates to an electronic connector and, more particularly, to a double visual-interface socket compliant with the Digital Visual Interface (DVI) standard.
2. Description of Related Art
With the advancement of technology, computer peripherals have become so diversified that the number of sockets provided in a computer must increase accordingly. In consequence, the so-called composite or stacked-type sockets were developed, wherein a plurality of sockets are stacked together three-dimensionally and integrated into a single socket, thereby not only reducing the footprint of the otherwise multiple sockets on a motherboard or interface card, but also simplifying the pin insertion procedure.
Please refer to FIG. 1 for a sectional view of a conventional stacked-type socket 10. The stacked-type socket 10 includes a housing 100. Socket units 11, 13, 15 are stacked in the housing 100 and include terminal pins 110, 130, 150, respectively. In order for the terminal pins 110, 130, 150 to pass through a bottom surface of the housing 100 and be subsequently inserted into guide holes of a connection port on a circuit board in a backend application, the terminal pins 130 of the middle socket unit 13 and the terminal pins 150 of the top socket unit 15 must be increased progressively in length, relative to the terminal pins 110 of the bottom socket unit 11.
Digital Visual Interface (DVI), a high-speed series interface standard dedicated to the transmission of digital and analog video signals, is intended to enhance the image quality of computer displays and has been widely used in various display devices such as flat panel displays and digital projectors. The Digital Visual Interface has a clock frequency ranging from 20 MHz to 165 MHz so as to achieve high resolution and meet the requirement of high-capacity, high-frequency transmission for large displays. In addition, the Digital Visual Interface allows a bandwidth up to 1.65 Gbps in a Single Link transmission mode, and over 2 Gbps in a Dual Link transmission mode. Therefore, strict requirements in high-frequency properties are specified in the DVI standard for connection cables and sockets which serve as signal transmission paths. To ensure signal quality, all DVI compatible products on the market must pass related tests and conform to specifications set forth in the DVI standard.
Presently, double visual-interface sockets have been successfully developed for dual-screen computer systems. However, if the aforesaid design of the conventional stacked-type sockets is applied to a double visual-interface socket, the terminal pins of the upper socket unit must be extended so as for bottom ends of these terminal pins, as well as those of the lower socket unit, to reach a solder surface at a bottom portion of the socket; as a result, the characteristic impedance of the resulting double visual-interface socket do not comply with related specifications.
In a high-frequency transmission system, it is a basic design requirement to achieve match of characteristic impedance between components. A mismatch of impedance between components will result in signal reflection, which in turn leads to production of noise and signal interference. As the lengths of terminal pins are a major factor in the characteristic impedance of a double visual-interface socket, it is a challenge faced by all socket designers to overcome the problem of impedance mismatch caused by the conventional stacked-type socket design.